Matt Lucas and Greg Davies for Doctor Who Christmas special

Matt Lucas and Greg Davies have been cast in the 'Doctor Who' Christmas special and will play Nardole and King Hydroflax respectively

Matt Lucas and Greg Davies are to appear in the 'Doctor Who' Christmas special.

While it's already known that Alex Kingston will be reprising her role as River Song in the festive episode, it's now been revealed Greg will be playing King Hydroflax while Matt has been cast as Nardole.

A synopsis of the episode reads: "It's Christmas Day on a remote human colony and the Doctor is hiding from Christmas Carols and Comedy Antlers.

"But when a crashed spaceship calls upon the Doctor for help, he finds himself recruited into River Song's squad and hurled into a fast and frantic chase across the galaxy.

"King Hydroflax is furious, and his giant robot bodyguard is out of control and coming for them all! Will Nardole survive? And when will River Song work out who the Doctor is?

"All will be revealed on a starliner full of galactic super-villains and a destination the Doctor has been avoiding for a very long time."

The news comes after showrunner Steven Moffat teased that River and the 12th Doctor, played by Peter Capaldi, will be a match made in heaven in the Christmas episode.

He explained: "The big deal is Doctor No 12 encountering River and vice versa. It's strange because they're now, in our human terms, the perfect couple. They're both sexy older people. It's always been slightly strange before with Matt Smith. Now, yeah, they could actually be married. It works."

Moffat added: "If you're a long-term fan of the show, you might be interested because there's been a lot of talk about the Doctor and River's glory years but we've never seen them. Here at last we seem them as Mr. and Mrs. Who at the height of their powers. It's great fun."